ENVIRSC 1G03 Lecture Notes - Lecture 9: Richter Magnitude Scale, Geomagnetic Reversal, Oceanic Crust

• School: McMaster University
• Department: Environmental Science
• Course: ENVIRSC 1G03
• Professor: Maureen Padden

Document Summary

Magnetic reversal = a switch in the earth"s magnetic field. Were detected in bands parallel to mors. Geologists were able to assign absolute dates for magnetic reversal. Using radioactive dating, the reversals can be dated from land-based volcanoes and then correlated to the sea-floor records. Long intervals of magnetic reversal are thicker than short periods. For magnetic reversals of short duration, narrow bands of ocean floor were detected and vice versa. The youngest magnetic reversal occurred at the mor"s, older reversals were found progressively farther away. Working backwards from modern igneous rocks, the banding pattern of magnetic reversals in the oceanic crust is dated according to the land-based volcanic record. Isochron contours connecting rocks of equal age. Oldest part of the oceanic crust is ~200 million years old. Magnitude 5 is 10 times larger than magnitude 4. Energy released increases 32 times for each magnitude. Strong earthquakes are around 5-6, great earthquakes are 7-8.